In the process of producing a semiconductor device such as IC and LSI, microfabrication by lithography using a photoresist composition has been conventionally performed. Recently, with increase in the integration degree of an integrated circuit, formation of an ultrafine pattern in the sub-micron or quarter-micron region is required. To cope with this requirement, the exposure wavelength also tends to become shorter, for example, from g line to i line or further to KrF excimer laser light. Furthermore, other than the excimer laser light, development of lithography using electron beam, X-ray or EUV light is proceeding at present.
In particular, the electron beam lithography is positioned as a next-generation or next-next-generation pattern formation technology, and a high-sensitivity and high-resolution positive resist is being demanded. Among others, elevation of the sensitivity is a very important task so as to shorten the wafer processing time, but in the positive resist for electron beam, there arises a problem that when elevation of the sensitivity is sought for, reduction of resolution is liable to occur.
In this way, high sensitivity is in a trade-off relationship with high resolution and further with good pattern profile, and it is very important how satisfy both of these at the same time.
Also in the lithography using X-ray or EUV light, it is similarly an important task to satisfy high sensitivity, high resolution and good pattern profile all at the same time, and this task needs to be solved.
In order to solve these problems, for example, in JP-A-9-179300 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”), International Publication No. 2005/23880, JP-A-2005-232396 and JP-A-2004-348014, a resist composition using a resin having an acetal-type protective group is disclosed, and it is supposed that the resolution and sensitivity are improved by the composition.
However, more improvements are required in the resolution and sensitivity and furthermore, in terms of pattern profile and exposure latitude (EL).